What’s up with hair? I mean, we see a bunch of commercials telling us how to take care of it and how to impress other people with it, but what is it made up of exactly?
What is hair?
Hair is actually composed of four components: the follicle, the shaft, the inner and outer sheaths.
The follicle is a tube-like structure located in our skin and it has two components: the papilla and the bulb. The papilla contains itty bitty blood vessels (called capillaries) which provide nutrients to a bundle of cells. This bundle of cells is referred to as the bulb. The cells in the bulb actually divide every 23-72 hours, which is faster than any other cell in our body!
The shaft is the part of the hair that is visible to us. It is composed of three layers dead, hard protein called keratin. The innermost layer is called the medulla and isn’t always present. The middle layer is the cortex, which makes up the majority of the shaft, and the outermost layer is the cuticle. The cuticle is formed by overlapping scales, somewhat like a roof.
The inner and outer sheaths
The follicle is surrounded by two sheaths, an inner and outer sheath, which help protect and mold the hair. The inner sheath ends just above the opening of the sebaceous gland (Remember those? They provide oil [sebum] to our skin and are found in the dermis layer of our skin!) and follows the rest of the shaft. The outer sheath encloses both the inner sheath and the follicle, and it ends just below the sebaceous gland.
And that’s the structure of hair! The follicle is similar to the roots of a plant in that it provides the nutrients and allows the hair to stay in the skin. Around the follicle are two sheaths, which wrap around it to add more stability and strength. Finally, the part we see everyday is known as the shaft of the hair. That’s all to it.
In the next few weeks, we’ll explore different topics involving hair like goosebumps, curly hair, the colour of hair, and greying hair! There will be a few random topics sprinkled in there too before things get too hairy.
Yes, that just happened.
Brannon, H. 2006. The biology of hair. About.com. <http://dermatology.about.com/cs/hairanatomy/a/hairbiology.htm> August 7th, 2013.